The present invention relates to a new and improved construction of a resistance welding machine for the seam welding of blanks or bodies, typically can bodies formed of sheet metal.
Generally speaking the resistance welding machine of the present development is of the type comprising a guide device arranged in front of the electrode rolls for producing an exactly fixed overlap of the edges of the blanks or bodies and for guiding the overlapped body edges to the weld point between the electrode rolls.
The welding rolls of seam welding machines must be machined after they have been used for a certain operating time, to insure that the electrode wire which travels thereon always is exactly guided.
Upon multiple machining of the welding rolls the radius thereof decreases more than one millimeter during the course of time. Consequently, there is always a shifting of the welding spot or point in relation to the body guiding means, specifically the overlapped body edges which enter the welding spot or point.
With conventional machines where there is utilized overlapping of the body edges by more than six times the gage or thickness of the sheet metal or plate, this slight displacement or shifting has little effect on the quality of the welded seam.
With the development of seam welding machines wherein the overlapping of the body edges is below six gage or thickness of the sheet or plate, even a very slight deviation of the welding spot or point from the ideal value leads to reduction in quality of the welded product, or, in fact, untight welding seams due to irregular overlapping along the blanks or bodies. The displacement of the overlapping body edges is caused by virtue of the fact that the overlapping, due to shifting of the welding spot, no longer tangentially merges therewith.
Therefore, attempts have already been made to overcome such shortcomings by inserting supports below the guide device. This work, however, requires much too much time and dexterity on the part of the operator, since with a one-time machining of the welding rolls there is removed only about 1/10 millimeter of material, so that the thickness of the support to be inserted amounts to less than 1/10 millimeters.